1. Field of the Invention
The present invention relates to the field of bus structures and methods.
2. Prior Art
I2C is a multi-master serial computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, an embedded system or a cellphone. The name stands for Inter-Integrated Circuit.
The System Management Bus (abbreviated to SMBus or SMB) is a simple two-wire bus used for communication with low-bandwidth devices on a motherboard, especially power related chips such as a laptop's rechargeable battery subsystem. Other devices might include temperature sensors and lid switches. A device can provide manufacturer information, indicate its model/part number, save its state for a suspend event, report different types of errors, accept control parameters, and return status. The SMBus is generally not user configurable or accessible. The bus was defined by Intel in 1995. It carries clock, data, and instructions and is based on Philips' I2C serial bus protocol. Its clock frequency range is 10 kHz to 100 kHz. Its voltage levels are different from those of I2C, but devices belonging to the two systems are often successfully mixed on the same bus. The SMBus has an extra optional signal called ALERT#, which can be used by slaves to send an interrupt request to the controller.
These two buses are bi-directional buses using a bi-directional clock line and a bi-directional data line, both pulled high by pull-up resistors unless pulled low by one or more devices on the bus. In general, the I2C bus and SMBus are compatible, but there are some subtle differences between the two. When devices are stacked, however, such as may be required in high-voltage battery stack monitors for example, the required support circuitry is expensive and large, requiring many optocouplers and microcontrollers to manage the pack-to-pack communication.
For reference purposes, The I2C-Bus Specification, version 2.1, January 2000 and the System Management Bus (SMBus) Specification version 2.0, Aug. 3, 2000 are incorporated herein by reference.